264 lines
8.1 KiB
Groff
264 lines
8.1 KiB
Groff
.\" Man page generated from reStructuredText.
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.TH "MPI_PROBE" "3" "Feb 14, 2025" "" "Open MPI"
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.sp
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\fI\%MPI_Probe\fP — Blocking test for a message.
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.SH SYNTAX
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.SS C Syntax
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.INDENT 0.0
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.INDENT 3.5
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.sp
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.nf
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.ft C
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#include <mpi.h>
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int MPI_Probe(int source, int tag, MPI_Comm comm, MPI_Status *status)
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.ft P
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.fi
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.UNINDENT
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.UNINDENT
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.SS Fortran Syntax
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.INDENT 0.0
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.INDENT 3.5
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.sp
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.nf
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.ft C
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USE MPI
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! or the older form: INCLUDE \(aqmpif.h\(aq
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MPI_PROBE(SOURCE, TAG, COMM, STATUS, IERROR)
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INTEGER SOURCE, TAG, COMM, STATUS(MPI_STATUS_SIZE), IERROR
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.ft P
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.fi
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.UNINDENT
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.UNINDENT
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.SS Fortran 2008 Syntax
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.INDENT 0.0
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.INDENT 3.5
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.sp
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.nf
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.ft C
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USE mpi_f08
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MPI_Probe(source, tag, comm, status, ierror)
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INTEGER, INTENT(IN) :: source, tag
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TYPE(MPI_Comm), INTENT(IN) :: comm
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TYPE(MPI_Status) :: status
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INTEGER, OPTIONAL, INTENT(OUT) :: ierror
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.ft P
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.fi
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.UNINDENT
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.UNINDENT
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.SH INPUT PARAMETERS
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.INDENT 0.0
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.IP \(bu 2
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\fBsource\fP: Source rank or \fBMPI_ANY_SOURCE\fP (integer).
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.IP \(bu 2
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\fBtag\fP: Tag value or \fBMPI_ANY_TAG\fP (integer).
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.IP \(bu 2
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\fBcomm\fP: Communicator (handle).
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.UNINDENT
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.SH OUTPUT PARAMETERS
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.INDENT 0.0
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.IP \(bu 2
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\fBstatus\fP: Status object (status).
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.IP \(bu 2
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\fBierror\fP: Fortran only: Error status (integer).
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.UNINDENT
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.SH DESCRIPTION
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.sp
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The \fI\%MPI_Probe\fP and \fI\%MPI_Iprobe\fP operations allow checking of incoming
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messages, without actual receipt of them. The user can then decide how
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to receive them, based on the information returned by the probe in the
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status variable. For example, the user may allocate memory for the
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receive buffer, according to the length of the probed message.
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.sp
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\fI\%MPI_Probe\fP behaves like \fI\%MPI_Iprobe\fP except that it is a blocking call that
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returns only after a matching message has been found.
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.sp
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If your application does not need to examine the \fIstatus\fP field, you can
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save resources by using the predefined constant \fBMPI_STATUS_IGNORE\fP as a
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special value for the \fIstatus\fP argument.
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.sp
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The semantics of \fI\%MPI_Probe\fP and \fI\%MPI_Iprobe\fP guarantee progress: If a call
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to \fI\%MPI_Probe\fP has been issued by a process, and a send that matches the
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probe has been initiated by some process, then the call to \fI\%MPI_Probe\fP
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will return, unless the message is received by another concurrent
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receive operation (that is executed by another thread at the probing
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process). Similarly, if a process busy waits with \fI\%MPI_Iprobe\fP and a
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matching message has been issued, then the call to \fI\%MPI_Iprobe\fP will
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eventually return \fIflag\fP = true unless the message is received by another
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concurrent receive operation.
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.sp
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\fBExample 1:\fP Use blocking probe to wait for an incoming message.
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.INDENT 0.0
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.INDENT 3.5
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.sp
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.nf
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.ft C
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CALL MPI_COMM_RANK(comm, rank, ierr)
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IF (rank == 0) THEN
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CALL MPI_SEND(i, 1, MPI_INTEGER, 2, 0, comm, ierr)
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ELSE IF(rank == 1) THEN
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CALL MPI_SEND(x, 1, MPI_REAL, 2, 0, comm, ierr)
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ELSE ! rank == 2
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DO i=1, 2
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CALL MPI_PROBE(MPI_ANY_SOURCE, 0,
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comm, status, ierr)
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IF (status(MPI_SOURCE) = 0) THEN
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CALL MPI_RECV(i, 1, MPI_INTEGER, 0, 0, status, ierr)
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ELSE
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CALL MPI_RECV(x, 1, MPI_REAL, 1, 0, status, ierr)
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END IF
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END DO
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END IF
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.ft P
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.fi
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.UNINDENT
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.UNINDENT
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.sp
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Each message is received with the right type.
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.sp
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\fBExample 2:\fP A program similar to the previous example, but with a
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problem.
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.INDENT 0.0
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.INDENT 3.5
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.sp
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.nf
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.ft C
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CALL MPI_COMM_RANK(comm, rank, ierr)
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IF (rank == 0) THEN
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CALL MPI_SEND(i, 1, MPI_INTEGER, 2, 0, comm, ierr)
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ELSE IF(rank == 1) THEN
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CALL MPI_SEND(x, 1, MPI_REAL, 2, 0, comm, ierr)
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ELSE
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DO i=1, 2
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CALL MPI_PROBE(MPI_ANY_SOURCE, 0,
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comm, status, ierr)
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IF (status(MPI_SOURCE) == 0) THEN
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CALL MPI_RECV(i, 1, MPI_INTEGER, MPI_ANY_SOURCE, &
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0, status, ierr)
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ELSE
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CALL MPI_RECV(x, 1, MPI_REAL, MPI_ANY_SOURCE, &
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0, status, ierr)
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END IF
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END DO
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END IF
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.ft P
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.fi
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.UNINDENT
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.UNINDENT
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.sp
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We slightly modified Example 2, using \fBMPI_ANY_SOURCE\fP as the source
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argument in the two receive calls in statements labeled 100 and 200. The
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program is now incorrect: The receive operation may receive a message
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that is distinct from the message probed by the preceding call to
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\fI\%MPI_Probe\fP\&.
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.SH ERRORS
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.sp
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Almost all MPI routines return an error value; C routines as the return result
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of the function and Fortran routines in the last argument.
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.sp
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Before the error value is returned, the current MPI error handler associated
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with the communication object (e.g., communicator, window, file) is called.
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If no communication object is associated with the MPI call, then the call is
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considered attached to MPI_COMM_SELF and will call the associated MPI error
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handler. When MPI_COMM_SELF is not initialized (i.e., before
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\fI\%MPI_Init\fP/\fI\%MPI_Init_thread\fP, after \fI\%MPI_Finalize\fP, or when using the Sessions
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Model exclusively) the error raises the initial error handler. The initial
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error handler can be changed by calling \fI\%MPI_Comm_set_errhandler\fP on
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MPI_COMM_SELF when using the World model, or the mpi_initial_errhandler CLI
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argument to mpiexec or info key to \fI\%MPI_Comm_spawn\fP/\fI\%MPI_Comm_spawn_multiple\fP\&.
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If no other appropriate error handler has been set, then the MPI_ERRORS_RETURN
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error handler is called for MPI I/O functions and the MPI_ERRORS_ABORT error
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handler is called for all other MPI functions.
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.sp
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Open MPI includes three predefined error handlers that can be used:
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.INDENT 0.0
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.IP \(bu 2
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\fBMPI_ERRORS_ARE_FATAL\fP
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Causes the program to abort all connected MPI processes.
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.IP \(bu 2
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\fBMPI_ERRORS_ABORT\fP
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An error handler that can be invoked on a communicator,
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window, file, or session. When called on a communicator, it
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acts as if \fI\%MPI_Abort\fP was called on that communicator. If
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called on a window or file, acts as if \fI\%MPI_Abort\fP was called
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on a communicator containing the group of processes in the
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corresponding window or file. If called on a session,
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aborts only the local process.
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.IP \(bu 2
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\fBMPI_ERRORS_RETURN\fP
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Returns an error code to the application.
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.UNINDENT
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.sp
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MPI applications can also implement their own error handlers by calling:
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.INDENT 0.0
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.IP \(bu 2
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\fI\%MPI_Comm_create_errhandler\fP then \fI\%MPI_Comm_set_errhandler\fP
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.IP \(bu 2
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\fI\%MPI_File_create_errhandler\fP then \fI\%MPI_File_set_errhandler\fP
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.IP \(bu 2
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\fI\%MPI_Session_create_errhandler\fP then \fI\%MPI_Session_set_errhandler\fP or at \fI\%MPI_Session_init\fP
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.IP \(bu 2
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\fI\%MPI_Win_create_errhandler\fP then \fI\%MPI_Win_set_errhandler\fP
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.UNINDENT
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.sp
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Note that MPI does not guarantee that an MPI program can continue past
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an error.
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.sp
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See the \fI\%MPI man page\fP for a full list of \fI\%MPI error codes\fP\&.
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.sp
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See the Error Handling section of the MPI\-3.1 standard for
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more information.
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.sp
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Note that per the “Return Status” section in the “Point\-to\-Point
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Communication” chapter in the \fI\%MPI Standard\fP, MPI errors on messages queried
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by \fI\%MPI_Probe\fP do not set the \fBstatus.MPI_ERROR\fP field in the
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returned \fIstatus\fP\&. The error code is always passed to the back\-end
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error handler and may be passed back to the caller through the return
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value of \fI\%MPI_Probe\fP if the back\-end error handler returns it.
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The pre\-defined MPI error handler \fBMPI_ERRORS_RETURN\fP exhibits this
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behavior, for example.
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.sp
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\fBSEE ALSO:\fP
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.INDENT 0.0
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.INDENT 3.5
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.INDENT 0.0
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.IP \(bu 2
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\fI\%MPI_Iprobe\fP
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.IP \(bu 2
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\fI\%MPI_Cancel\fP
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.UNINDENT
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.UNINDENT
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.UNINDENT
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.SH COPYRIGHT
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2003-2025, The Open MPI Community
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.\" Generated by docutils manpage writer.
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.
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